C-V testing on AAO electrostatic capacitors

The main performance of capacitor is store charge. Under the power supplied by the outer circuit. On the two electrodes gathered the same amount charge which have opposite charge.

When we withdraw the power source. The charge would store in the electrode. Except the property of capacitance. The capacitor also have the inductance and resistance properties.

Under the low frequency signal, Inductance and resistance characteristics influence on the device can be ignored. But under the high frequency signal, Resistance and inductance characteristics will lead to capacitance dissipation. Aimed to test the characteristics of the capacitor. In my article I mainly used cyclic voltammetry to test the C-V curve and I-V curve and the cycle-to-cycle stability.

We used Zahner IM6 Electrochemical workstation to test all the parameters. And we chose two electrode mode to test the electrostatic capacitor as show in figure 5-1.

There three types of electrostatic supercapacitor we would test. The first one is the top side of AAO substrate with gold layer. The gold layer based on AAO porous structure is one of the electrode in this device, and the other one is the aluminum which had not reacted with the electrochemical solution. These two metal layer were the electrode of the capacitor. For the second one. We know during the AAO fabrication. We use electrochemical etching to make the hexagonal structures, in the back side of the sample, there were also have the porous structures, but it has the shallow holes in that side. So after sputtering gold on this side. It also can use as one electrodes. We can use this side and the aluminum as the other capacitor which maybe have smaller capacitance than the first one. This speculation need the test result to approve. And the third one is that when we continue to expand the

Figure 5-1: the Zahner IM6 Electrochemical workstation

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capacitance of the electrostatic supercapacitor. In the basis of high aspect ratio, we can try

to increase the effective area in the other way. The parallel approach of the electrode was a well chosen based on the porous structure which we have mentioned in the design part of this article. In this process we should use ALD technology which we did not have in our lab, so I try to solve this problem in the other way. We can connect the top side and back

side together and let this connected part as one electrode, and the aluminum layer between Figure 5-3: the C-V capacitance change under the different sweep rate

Figure 5-2: the C-V curve of electrostatic capacitor under the different sweep rate

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them as the other electrode. These two electrodes formed a capacitor which can be equivalent to the two capacitors connect in parallel. And then test the properties of this capacitor. Find the relationship of the performance between shunt capacitor and the single one, such as the theoretical value, and loss. All of these test would provide the theoretical and data basis for future research when we fabricate capacitor in parallel connect based on AAO substrate. For the single layer supercapacitor based on AAO substrate has been published in Nature Nanotechnology 2009[5]. So for the multilayer supercapacitor based on AAO substrate can greatly increase the capacitance in this field. Therefore, this research had the great significance.

We used Zahner IM6 Electrochemical workstation to test the samples, the frequency we set 1 kHz, the voltage sweep range from 0-2V, and the sweep rate we used5mv/s, 40mv/s, 100mv/s, 200mv/s, 300m/s and 400mv/s. And then we choose two electrodes mode. In order to get a stable capacitance, the cycle we chose 3. And the sample point we chose 200.

After the test we used the software of origin 8.0 to analyze the data and got the result as show in figure 5-2. From the image of the test result, under the different sweep ratio from 5mv/s to 300mv/s. All the cyclic voltammetry curve have the well rectangle characters.

That means these capacitor have a very stable capacitance characteristics. It fit for using the large current and high power to charge and discharge it in a certain extent. This capacitor had the capability in using large current charge and discharge. In order to get the specific capacitance of the capacitor, we used origin 8.0 integrate the area of C-V curve under different conditions. And then used formula 5.2.5 to calculate the capacitance per square centimeter. And then also used origin 8.0 draw the figure which illustrate the capacitance change under different sweep rate. From the figure 5-3, we can see the

Figure 5-4: the impedance change and the absolute value of phase

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capacitance have a significant decrease coupled with the sweep rate increase. The reason can be summed up like that there were so many porous structure in the surface of the electrode. There are also have some island structure when we use sputtering to deposit gold on the porous structure. That means somewhere of the electrode connected not very well.

Under the quickly charge condition, there have not enough space and time which can used for ions go in and out. Not everywhere of the electrode layer effectively utilize. So there have a change under different scan rate.